The invention pertains to the field of scanning radio receivers.
This type receiver can be made to automatically scan a given band of frequencies and will stop at the first station encountered that is of adequate signal strength. Upon loss of the signal, scanning resumes until the next station of the requisite signal strength is received. Scanning normally occurs over a public service band wherein adjacent stations are closely situated within the frequency separation so that the receivers must have good frequency selective characteristics. For such scanning operation it is usual to employ a number of quartz crystals sequentially connected into the local oscillator circuit for changing the local oscillator frequency and, correspondingly, providing scan tuning of the receiver in accordance with whatever valued crystals are employed. Crystals are relatively expensive and, therefore, most scanning receivers presently sold are high cost items. There is a further disadvantage in the requirement that a particular frequency crystal be obtained for each station to be scan, since there are thousands of stations in the public service band of 148 to 176 MHz each requiring a different crystal.
Another scanning radio receiver employs a crystal controlled oscillator with a single crystal, wherein multiple local oscillator frequencies are generated by means of rather complex logic circuitry. This type of receiver is also costly.